Self-regulating reciprocating action fuel injection pump



Jan. 17, 1961 P. E. BESSIERE SELF-REGULATING RECIPROCATING ACTION FUEL INJECTION PUMP Filed Dec. 3, 1957 5 Sheets-Sheet 1 MN T INVE/V TOR "PIERRE ETIENNE pass/m?! Jan. 17, 1961 E BES' R 2,968,247

SELF-REGULATING RECIPROCATING ACTION FUEL INJECTION PUMP Filed Dec. 3, 1957 3 Sheets-Sheet 2 NVE N TOR Jan. 17, 1961 P. E. BESSIERE SELF-REGULATING RECIPROCATING ACTION FUEL INJECTION PUMP Filed Dec. 3, 1957 I; a 8 5 739 T:

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3 Sheets-Sheet 3 NVE N TOR want Zr 3 ATTORNEXE United States SELF-REGULATING RECIPROCATING ACTION FUEL INJECTION PUMP PierreEtieune Bessiere, 55 Blvd. du Commandant Charcot, Neuilly-sur-Seine, France Filed Dec. 3, 195 7, Ser.'No. 700,426

Claims priority, application France Dec. 13, 1956 12 Claims. (Cl.'103-37) The present invention relates to 'self-regulating reciprocating action pumps and in particular piston pumps, that is to say to pumps such that the delivery rate per cycle decreases when the speed at which the pump is driven increases, at least within "some ranges of speed of operation. My invention is more particularly but not exclusively concerned with fuel injection pumps for internal combustion engines.

The object of my invention is to provide a pump of this kind which is better adapted to meetth'e requirements of practice than those existing at the present time.

According to my invention, 1 provide a discharge conduit through which a portion of the liquid displaced by the pump piston during its delivery stroke can escape to the outside, and this discharge conduit is controlled by a valve member movable between a first end position and a second end position so that it opens the discharge conduit for a portion of the stroke of said valve and that it closes said conduit for the other portion of said stroke and that, on every cycle of the pump, said valve member is brought to its first end position, against a return force exerted for instance by a spring, through means, preferably hydraulic, pneumatic or electro-magnetic, which cease to act at least approximately when the pump piston starts on its delivery stroke, this valve member being subjected to the action of braking means, in particular of the dash-pot type, during its movement from its first end position toward its second end position produced by the action of said return force.

\ Preferred embodiments of my invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

Fig. 1 is a diagrammatic axial sectional view of a fuel injection pump made according to a first embodiment of my invention. 7

Fig. 2 is a similar view showing the pants in difierent relative positions.

Figs. 3 and 4 are views, similar to Fig. .1, of an in jection pump made according to two other embodiments of my invention.

Fig. 5 shows a modification of the pump illustrated by Fig. 4.

The pump includes a cylinder 1 in which moves a piston 2 which is given a reciprocating motion through any suitable means, for instance a cam, not shown. The piston is shown in the position close to its outer dead center position on Figs. 1, 3 and 4. This piston controls an orifice 3 through which a feed conduit 4 opens into cylinder 1. This conduit 4 is supplied with fuel under relatively low pressure, for instance by means of an auxiliary pump which collects fuel from a tank (these two elements being not shown). The portion of cylinder 1 located above orifice 3 constitutes the delivery chamber 5 of the pump. This chamber is provided with a delivery orifice 6 connected, through a conduit 7 (which may include a check-valve 8), with the injector or injectors (not shown) to be supplied by the pump. Piston 2 is provided with a channel 9 opening atone end into chamber 5 and at the other end, through anorifice 9a, into the side wall of said piston so as to be able to cooperate with a conduit 10 opening into cylinder 1 at a level such that chamber 5 is connected therewith through conduit 9 before piston 2 reaches its upper (inner) dead center position.

In such a pump, if no other means were provided, the delivery rate per cycle would be constant and equal to the volume of fluid displaced by the piston between the time when it closes the orifice 3 and the time when cham her 5 is connected with discharge conduit 10-.

in order to obtain a self-regulating pump according to my invention, I provide a fuel discharge conduit 11 starting from delivery chamber 5 and through which flows the excess of fuel. This conduit 11 is controlled by a reciprocating valve member movable between a first end position and a second end position so that it opens the discharge conduit for a portion of the s'troke of said valve and it closes it forth e other portion of said stroke and that, on every cycle of thepump, said valve memher is brought to its first end position, against a return force exerted for instance by a spring, through means, preferably hydraulic, pneumatic or electro-magnetic, which cease to act at least approximately when the pump piston starts on its delivery stroke, this valve member being subjected to the action of braking means, in particular of the dash-pot type, during its displacement from its first end position toward its second end position produced by the action of said return force.

It will be understood that, with such an arrangement, the duration of the return stroke of the valve member is constant and that the beginning of the useful "delivery stroke resulting from the closing of the discharge conduit is the more delayed as'the speed of the pump is higher.

As shown by the drawings, the valve member may be a slide valve 12 housed in a cylindrical housing 13 in which it may move between two 'end positions determined by abutments 14 and 15. This slide valve 12 is urged toward abutment 15 by a spring 16. It includes two cylindrical portions 12a and 12b leaving between them a groove of relatively great height. The fuel discharge conduit 11 extends through cylindrical housing 13 at a level such that the two portions of said conduit 11 located on respective sides of said housing are in free communication with each other through groove 120 ,during most of the stroke which brings slide valve 12 from each other by the cylindrical portion 12a of the slide valve during the end of this snake (Fig. 2).

Advantageously, the means for displacing slide valve 12 on every cycle are constituted by a source of liquid under pressure capable of sending this liquid into a chamber of the slide valve-housing limited by 'an end wall of the slide valve, and this source is made to supply this liquid periodically in synchronism with the displacemerit of piston 2.

According to a first embodiment, I make use of a source at a substantially constant pressure and the conduit connecting this source with said chamber is controlled by distributing valve means operated in synch'ronism with piston 2, so as to stop the inflow of liquid substantially at the same time as piston 2 closes the feed orifice 3. Preerably, said distributing valve means is constituted by the piston 2 itself.

The above mentioned braking system may be consti-' tuted by providing the chamber above'referred to a leak or fluid discharge conduit having an orifice of reduced cross-section, capable of slowing down the new 3 of the liquid from the chamber when the slide valve is pushed by spring 16.

Preferably, the source of liquid under pressure is the auxiliary pump above referred to and the fuel supplied by said pump is advantageously conveyed through conduit 4.

For this purpose, as shown by Figs. 1, 2 and 3, 1 connect through a conduit 17, preferably provided with a check-valve 17a, conduit 4 with the chamber 13a of housing 13 that is limited by the end Wall of portion 12b of the slide valve. Piston 2 is provided with a groove 18 and the two portions of conduit 17 extending on opposite sides of cylinder 1 are placed in communication with each other by said groove 18 when piston 2 is in the vicinity of its lower dead center position (Figs. 1 and 3). On the contrary, when piston 2 moves away from this dead center position (Fig. 2), the two portions of conduit 17 are separated from each other. Chamber 13a communicates with a fluid discharge conduit section 19 provided with throttling means 20 which are preferably adjustable.

In order to reduce to a minimum the time of closing of discharge conduit 11 by slide valve 12, this slide valve is arranged in such manner as to place chamber 13a in communication with a fluid discharge conduit section 21 as soon as portion 12a begins to project into conduit 11. It sufilces for this purpose to provide slide valve 12 with a conduit 22 opening at one end into chamber 13a and at the other end, through an orifice 22a, into the side wall of one of the portions 12a and 12b of the slide valve, said orifice cooperating with a groove 21a provided at a suitable height in housing 13 and which constitutes one of the ends of conduit 21. Of course, conduit 22 and the discharge conduit means (groove 21a, conduit 21, etc.) must be so arranged as to permit a free discharge of the fuel contained in housing 13a when orifice 22a comes opposite groove 21a at the end of the downward movement of slide valve 12, but they must at least partly prevent outfiow of the fuel fed to push slide valve 12 against its abutment 14.

If it is supposed for instance that conduits 10, 19 and 21 are connected to a conduit 23, said conduit 23 may be divided into two portions both opening into cylinder 1, piston 2 being provided with a longitudinal groove 24 such that these two portions of conduit 23 are separated from each other by piston 2 when said piston is in the vicinity of its lower dead center position (conduit 17 being opened) but that said portions of conduit 23 are connected together by groove 24 when piston 2 moves away from said lower dead center position (conduit 17 closed, downward movement of the slide valve braked). According to a modification illustrated by Fig. 4, conduit 23 might be let permanently opened. In this case, conduit 22 is made of a diameter sufficiently great to oppose only a negligible resistance to the fiow at low pressure of fuel under the action of spring 16, but sufiiciently small to oppose a substantial resistance to the flow of fuel at relatively high pressure coming from conduit 4 and intended to bring slide valve 12 into its first end position, where it is applied against its abutment 14.

In order to obtain a sufficient pressure of the liquid collected from feed conduit 4, I may either provide a throttled portion 25 of said conduit 4 downstream of the point where conduit 17 branches off therefrom (Figs. 1 and 2), or arrange piston 2 so that, after said piston coming close to its lower dead center position has opened orifice 3 for a time sufficient to permit the filling of chamber 5, it again closes orifice 3 (Fig. 3).

In this last mentioned construction, I provide in piston 2 a groove 26 communicating with chamber through a conduit 27, and the stroke of this piston is adjusted in such manner that, when it is coming close to its lower dead center position (shown by Fig. 3), orifice 3 is first opened by groove 26 and thus brought into communication with chamber 5 for a time sufiicient to permit of said chamber being filled with liquid, and then once more closed so that the whole of the liquid coming from the auxiliary pump is then directed toward the chamber 13a of the slide valve housing.

Advantageously the pump according to my invention further includes a device for adjusting the duration of the return movement of slide valve 12 toward its seat 15, the operation of this device being based upon the action of the throttled passage 20 obtained by means of screw 28 and/or upon the initial tension of spring 16 adjusted by means of a threaded plug 29. Chamber 131:, which is located in housing 13 between the end face of portion 12a and plug 29, may be provided with an orifice 30 capable of collecting the fuel which may have leaked past the portion 12a of the slide valve.

Such a pump works as follows.

It will be supposed that piston 2, moving in the downward direction, is getting close to its lower dead center position shown by Fig. 1, the slide valve being then in the lower position illustrated by Fig. 2. Conduit 4 supplies liquid into delivery chamber 5, which is filled with this liquid. Simultaneously with this, or, better, with a slight delay which permits of filling chamber 5 under full pressure, feed conduit 4 supplies liquid to the chamber 13a of cylindrical housing 13, through conduit 17 which is opened by groove 18, check-valve 17a being then lifted away from its seat. Chamber 13a is then in communication with conduit 23 through conduit 22, provided in the slide valve, and conduit 21 on the one hand, and also through conduits 19 (which is throttled at 20) and 10 on the other hand, but at this time conduit 23 is stopped by piston 2. Consequently, the liquid flowing into chamber 13a moves slide valve 12 upwardly so as to apply it against its upper abutment 14, as shown by Fig. 1. The fuel discharge conduit 11 of chamber 5 is then fully opened.

When piston 2 starts moving upwardly, it closes first conduit 17, then orifice 3. Chamber 13a ceases to be fed with liquid under pressure and slide valve 12 moves downwardly under the action of spring 16, this movement causing fuel to be forced through fluid discharge conduit section 19 and conduit 23, which is then opened by groove 24 whereas conduit 21 is closed. The movement of the slide valve is then braked by the throttled portion 20 of conduit 19. During this time, the liquid contained in chamber 5 is discharged through conduit 11. When the lower edge of the side orifice 22a of conduit 22 reaches the level of the upper edge of groove 21a, the throttled portion 20 begins to be short-circuited. Slide valve 12 is accelerated more and more as orifice 22a is being cleared. Finally, slide valve 12 moving at full speed (the throttled portion 20 being then wholly short-circuited) closes fuel discharge conduit 11. The discharge of liquid to the outside is thus suddenly stopped and liquid is then delivered from chamber 5 toward conduit 7. Injection starts as piston 2 has already moved through a portion b of its delivery stroke a (position shown in solid lines on Fig. 2). Injection stops when the side orifice 9a of conduit 9 (provided in piston 2) comes opposite conduit 10. Fuel delivery through conduit 7 is then finished and injection is sharply stopped (position shown in dot-and-dash lines on Fig. 2).

The delivery rate of the pump is proportional to the distance (a-b) for which fuel is delivered through conduit 7. Now, distance b is travelled over during the time taken by slide valve 12 to come to close fuel dis charge conduit 11 after conduit 17 has been closed. This time is constant. Consequently, when the speed of the engine increases, distance I) also increases and the delivery of the pump, which is proportional to (a-b) decreases. A self regulation is thus obtained.

If the speed further increases, a time comes when slide valve 12 is no longer given time to close fuel discharge conduit 11 before the orifice 9a of conduit 9 comes opposite conduit 10. The delivery of the pump then becomes zero and the speed at which this takes place is a limit speed which cannot be exceeded by the engine. v

According to another embodiment of my invention, the source of liquid under pressure intended to produce the displacement of slide valve 12 is an auxiliary reciprocating pump working in synchronism with the main pump 1, 2. I

As shown by Fig. 4, this auxiliary pump may be constituted by a cylinder 31 in which moves a piston 32 driven in such manner that it is in its upper dead center position when piston 2 is in its lower dead center position and vice versa, cylinder 31 being connected with chamber 13a by a conduit 17 which, in this case, is merely provided with a check-valve 17a. The volume delivered by piston 32 being generally greater than the volume delivered by slide valve 12, it may be useful to provide on conduit 17, upstream of check-valve 17a, a discharge valve (not shown) intended 'to permit outflow of the excess of liquid on every cycle. The other elements of Fig. 4 are identical with those of the preceding figures and therefore will not be described in detailed fashion. Cylinder 31 is supplied with liquid through a conduit 4a analogous to conduit 4. Discharge conduit 11, instead of branching oflf directly from delivery chamber 5, starts from conduit 7, upstream of checkvalve 8; a second check-valve 33 is provided in conduit 7 upstream of the point where conduit 11 branches off from said conduit 7. Check-valve 33 is adjusted to open under a pressure substantially lower than check-valve 8.

Finally, a check-valve 34 is provided in discharge conduit 11 between the housing 13 of slide valve 12 and the main discharge conduit 23. p

The operation of the pump illustrated by Fig. 4 is as follows.

It will be supposed that piston 2 moving in the downward direction is getting close to its lower dead center position shown by Fig. 3, the slide valve being then in the lower position (not shown) against abutment 15. Simultaneously, piston 32 is reaching its upper dead center position and delivers fuel, which has been fed through conduit 4a, past check-valve 17a into chamber 13a. In view of the choice of the diameter of conduit 22, which is very small with respect to the volume of fuel delivered by piston 32, only a very small amount of the inflowing fuel is allowed to escape through conduit 22 and the infiowing fuel remains under a pressure of for instance 20 kg./sq. cm. and therefore pushes slide valve 12 into the position shown by Fig. 4. At the same time, chamber is filled with fuel through conduit 4. Then piston 2, moving upwardly in cylinder 1 from its lower dead center position shown by the drawing, first closes orifice 3. The fuel delivered by piston 2 lifts checkvalve 33 but not check-valve 8 due to the different strengths of the springs of said check-valves. This fuel therefore escapes through conduit 11 in view of the fact that slide valve 12 is in its upper position. This fuel escapes toward the fuel tank past check-valve 34, through discharge conduit 23. Slide valve 12 moves downward at a slow rate because the liquid contained in chamber 13a must pass through the throttled passage 20 provided by screw 28 so as to escape through conduit 19 and conduit 23. At the end of a given time period, conduit 22 provided in slide valve 12 comes into communication with groove 21a, which causes chamber 13a to be suddenly emptied due to the fact that the throttled passage 20 is short-circuited. Slide valve 12 therefore gathers speed under the action of its spring 16 and suddenly closes conduit 11 which causes, as in the above described embodiment, the beginning of injection.

Conduit 22, although it is of reduced cross-section, is in this case sufficient to permit a quick downward movement of slide valve 12 because the volume of fuel which passes therethroug-h from chamber 13a is at "6 least ten times smaller than the volumedelivered by ,piston 32 for a shorter time when slide valve 12 was moved upwardly, so that the pressure in chamber 13a does not exceed for instance 3 kg./ sq. cm.

Injection stops when the conduit 9 of piston 2 comes opposite conduit 4 (fed under low pressure), which then plays the same part as the conduit 10 of Figs. 1 to 3, which produces in chamber 5 the pressure drop necessary to stop injection. The regulating effect is the same as in the case of Figs. 1, 2 and 3.

In the device illustrated by Fig. 5, the auxiliary pump 31, 32 serves not only to control slide valve 12 but also as an auxiliary pump feeding fuel to the main pump cylinder 1. For this purpose, the feed conduit 4 of cylinder 1 branches off from conduit 17 at a point there of downstream of check-valve 17a, and a check-valve 42 is inserted in this conduit 4. Furthermore, the diameters of piston 32 and cylinder 31 of the auxiliary pump are sufficiently great to enable piston 32, during its upward stroke, still to deliver a sufficient amount of fuel into cylinder 1 after the piston 2 of the main pump has cleared, in the course of its downward stroke, the orifice 3 of the feed conduit 4.

The cams or other means serving to actuate pistons 2 and 32 are arranged in such manner that piston 2, after it has cleared orifice 3, leaves this orifice open for a time, during which piston 32, moving toward its upper dead center position, delivers fuel into cylinder 1.

In the arrangement illustrated by Fig. 5, conduits 19 and 21 are controlled by an element 35 which is advantageously in the form of a slide valve provided with two grooves 35a and 35b, this slide valve being movablein a housing 36 between two end positions one of which (shown by the drawing) is determined by an abutment 37, whereas the other one is determined by a shoulder 38. Slide valve 35 is brought into the position shown by Fig. 5, where it closes both of said conduits 19 and 21,

by the liquid placed under pressure in cylinder 31 by piston 32 and fed under slide valve 35 through a conduit 40. On the contrary, the return stroke of slide valve 35, which brings it into the position where its grooves 35a and 35b clear conduits 19 and 21, is produced by a return spring 39.

I have further provided, in communication with the delivery chamber of cylinder 31, a safety valve 41 which enables a possible excess of fuel delivered by piston 32 to be discharged to the outside.

The strength of the spring of check-valve 42 is sufiicient to cause slide valves 12 and 35 to remain in their upper positions during the period for which piston 32 delivers liquid into cylinder 1.

It should be noted that the arrangement according to which the reciprocating auxiliary pump serves both to bring slide valve 12 into its upper position and to supply fuel to the cylinder of the main pump may be applied in all cases where the piston 32 of the auxiliary pump has a movement offset, at least approximately, by with respect to the movement of the piston 2 of the main pump, and this whatever he the distribution of the periods of closing of discharge conduit 11 by slide valve 12 with respect to the movement of the piston 2 of the main pump.

It should be noted that feed conduit 4 might be merged with the discharge conduit 11 and disposed in the upper portion of chamber 5, as indicated on the drawing for said discharge conduit 11. I

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limitedtheret'o as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims,

What I claim is:

l. A reciprocating action liquid pump which comprises, in combination, means including a fixed part and a movable part having a reciprocating displacement with respect to said fixed part for forming a varying volume space, a delivery conduit leading from said space, a fuel discharge conduit leading from said space, a reciprocating valve member associated with and movable across said fuel discharge conduit between a first end position and a second end position, said valve member being mranged to clear said fuel discharge conduit for the portion of its reciprocating movement ending in, and starting back from, said first end position and to close said fuel discharge conduit for the remainder of said reciprocating movement, resilient means operatively associated with said value member for urging said valve member toward said second end position thereof, means operatively connected to said movable part and said valve member operative in response to the movement of said movable part for moving said valve member to its first end position on every cycle of the pump, said last mentioned means being arranged to cease to act on said valve member at least approximately when said movable part starts on its movement which reduces the volume of said variable volume space, and means operatively associated with said value member for braking the movement of said valve member from said first end position thereof toward said second end position.

2. A reciprocating action liquid pump which comprises, in combination, means including a cylinder and a piston having a reciprocating displacement in said cylinder for forming a varying volume space therein, a delivery conduit leading from said space, a fuel discharge conduit leading from said space, a reciprocating valve member associated with and movable across said fuel discharge conduit between a first end position and a second end position, said valve member being arranged to clear said fuel discharge conduit for the portion of its reciprocating movement ending in, and starting back from, said first end position and to close said fuel discharge conduit for the remainder of said reciprocating movement, resilient means operatively associated with said valve member for urging said valve member toward said second end position thereof, means operatively connected to said movable part and said valve member operative in response to the movement of said pump piston for moving said valve member to its first end position on every cycle of the pump, said last mentioned means being arranged to cease to act on said valve member at least approximately when said pump piston starts on its delivery stroke, and means operatively associated with said valve member for braking the movement of said valve member from said first end position thereof toward said second end position.

3. A pump according to claim 1 in which said braking means are adjustable.

4. A pump according to claim 1 in which said resilient means are adjustable.

5. A reciprocating action liquid pump which comprises, in combination, means including a cylinder and a piston having a reciprocating displacement in said cylinder for forming a varying volume space therein, a delivery conduit leading from said space, a fuel discharge conduit leading from said space, fixed means forming a cylindrical housing through which said fuel discharge conduit extends, a reciprocating slide valve movable in said housing across said fuel discharge conduit between a first end position and a second end position, said slide valve being arranged to clear said fuel discharge conduit for the portion of its reciprocating movement ending in, and starting back from, said first end position and to close said fuel discharge conduit for the remainder of said reciprocating movement, resilient means operatively connected with said slide valve for urging said slide valve toward said second end position thereof, one end of said housing forming with said slide valve a variable volume chamber such that expansion thereof moves said slide valve toward said first end position thereof, a source of fluid under pressure, means connecting said source and said chamber for feeding fluid from said source to said chamber on every cycle of the pump, said last mentioned means being arranged to stop the feed of said fluid from said source to said chamber at least approximately at the beginning of every delivery stroke of said pump piston, and a fluid discharge conduit connected with said chamber for the outflow of fluid therefrom during the return movement of said valve member toward its second end position, said fluid discharge conduit including a throttled portion to brake said return movement.

6. A pump according to claim 5 in which said housing has a cylindrical wall further including a by-pass conduit forming a connection between the cylindrical wall of said housing and a point of said fluid discharge conduit on the other side of said throttled portion from said chamber, said slide valve being provided with a conduit opening at one end in the end wall of said slide valve and at the other end in the cylindrical Wall of said slide valve so as to by-pass said throttled portion after said slide valve has moved a given distance on its return movement.

7. A reciprocating action liquid pump which comprises, in combination, means including a cylinder and a piston having a reciprocating displacement in said cylinder for forming a varying volume space therein, a delivery conduit leading from said space, a fuel discharge conduit leading from said space, fixed means forming a cylindrical housing, a reciprocating slide valve movable in said housing across said fuel discharge conduit between a first end position and a second end position, said slide valve being arranged to clear said fuel discharge conduit for the portion of its reciprocating movement ending in, and starting back from, said first end position and to close said fuel discharge conduit for the remainder of said reciprocating movement, resilient means operatively connected with said slide valve for urging said slide valve toward said second end position thereof, one end of said housing forming with said slide valve a variable volume chamber such that expansion thereof moves said slide valve toward said first end position thereof, a source of fluid under pressure, means connecting said source and said chamber controlled by said pump piston for feeding fluid from said source to said chamber on every cycle of the pump during the suction stroke of said pump piston, at the latest when it is nearing the end of said stroke, said last mentioned means being arranged to stop the feed of said fluid from said source to said chamber at least approximately at the beginning of every delivery stroke of said pump piston, and a fluid discharge conduit connected with said chamber for the outflow of fluid therefrom during the return movement of said valve member toward its second end position, said fluid discharge conduit including a throttled portion to brake said return movement.

8. A pump according to claim 7 in which said fluid is a liquid and said source is a pump supplying liquid at a substantially constant pressure.

9. A pump according to claim 7 in which said fluid is the same liquid as that delivered by said pump and said source is another pump supplying said liquid at a substantially constant pressure, said pump cylinder being provided with a feed conduit opening at one end into said cylinder and the other end of which is connected with said source, said means for feeding fluid from said source to said chamber including a conduit branching off from said feed conduit at a point thereof, said feed conduit having a check valve between said point and said first mentioned end thereof opening towards said cylinder.

10. A pump according to claim 5 including means carried by said pump piston for controlling the discharge of said fluid during the return movement of said valve member.

11. A pump according to claim 5 in which said source of fluid under pressure is an auxiliary reciprocating action pump, said last mentioned pump being driven so that its piston reaches its upper dead center position when the main pump piston is at least approximately in its lower dead center position and vice versa.

12. A pump according to claim 11 in which the delivery of said auxiliary pump is connected with the main pump cylinder to supply it with liquid.

References Cited in the file of this patent UNITED STATES PATENTS 1,630,957 Lundstrom May 31, 1927 2,173,813 Bischof Sept. 19, 1939 2,279,010 Nichols Apr. 7, 1942 2,281,045 Outin Apr. 28, 1942 

